Method and recovery of benzene and toluene

ABSTRACT

A METHOD OF RECOVERING BENZENE AND TOLUENE FROM NORMALLY LIQUID HYDROCARBON MIXUTRTES CONTAINING IN EXCESS OF 50% OF BENZENE AND TOLUENE, TOGETHER WITH ACYCLIC MONO- OELFINS, ACYCLIC DIOLEFINS, CYCLO - PARAFFINS, CYCLIC MONO-OLEFINS, CYCLIC DIOLEFINS, AND IN SOME CASES, SULFUR AND NITROGEN OR OXYGEN COMPOUNDS, INCLUDING DISTILLING THE MIXTURE TO RECOVER A FRACTION BOILING IN THE BENZENETOLUENE RANGE, SUBJECTING THIS FRACTION TO A HYDROGEN TREATMENT IN THE PRESENCE OF A CATALYST AND UNDER CONDITIONS TO DEHYDROGENATE ACYCLIC DIOLEFINS AND HYDROGENATE ACYCLIC MONO-OLEFINS, POLYMERIZING THE HYDROGENATION PRODUCT, IF DESIRED, DISTILLING THE POLYMER PRODUCT TO RECOVER A FRACTION BOILING IN THE BENZENE-TOLUENE RANGE, SUBJECTING THE BENZENE - TOLUENE FRACTION TO A HYDROGEN TREATMENT IN THE PRESENCE OF A CATALYST AND UNDER CONDITIONS SUFFICIENT TO CONVERT NON-AROMATIC CYCLIC COMPOUNDS TO AROMATIC COMPOUNDS AND CRACK OTHER NON-AROMATIC COMPOUNDS OF LOWER BOILING POINT.

Dec. 11, 1973 s. M. KOVACH UAL 3,773,484-

METHOD AND RECOVERY OF BENZENE AND TOLUENE Original Filed Sept. 28, 1966(D o St 10 O-LOI---J-l Faed Mifure 3,778,484 METHOD AND RECOVERY OFBENZENE AND TOLUENE Stephen M. Kovach, Ashland, and Ralph E. Patrick,Flatwoods, Ky., assgnors to Ashland Oil, Inc., Columbus, Ohio Originalapplication Sept. 28, 1966, Ser. No. 582,652, now abandoned. Divided andthis application July 19, 1971, Ser. No. 163,631

Int. Cl. C07c 7/04 U.S. Cl. 260-674 R 2 Claims ABSTRACT OF THEDISCLOSURE A method of recovering benzene and toluene from normallyliquid hydrocarbon mixtures containing in excess of 50% of benzene andtoluene, together with acyclic mono olens, acyclic diolefins, cycloparaflins, cyclic mono-olens, cyclic diolefns, and in some cases, sulfurand nitrogen or oxygen compounds, including distilling the mixture torecover a fraction boiling in the benzenetoluene range, subjecting thisfraction to a hydrogen treatment in the presence of a catalyst and underconditions to dehydrogenate acyclic diolens and hydrogenate acyclicmono-olefins, polymerizing the hydrogenation product, if desired,distilling the polymer product to recover a fraction boiling in thebenzene-toluene range, subjecting the benzene toluene fraction to ahydrogen treatment in the presence of a catalyst and under conditionssuilicient to convert non-aromatic cyclic compounds to aromaticcompounds and crack other non-aromatic compounds of lower boiling point.

RELATED APPLICATIONS This application is a division of our copendingapplication Ser. No. 582,652, liled Sept. 28, 1966, now abandoned.

The present invention relates to the separation of aromatichydrocarbons. In a more specific aspect, the present invention relatesto the separation of normally liquid hydrocarbon mixtures containing atleast about 50% by volume of aromatics. In a still more speciiic aspect,the present invention relates to the recovery of benzene and toluenefrom normally liquid hydrocarbon mixtures containing at least about 50%by volume of aromatics.

Normally liquid hydrocarbon mixtures containing in excess of about 50%of benzene and toluene are commercially available from a variety ofsources. These mixtures contain, in addition to the benzene-toluene,acyclic mono-oleus, including, secondary and tertiary monooleins ofnormal and branch chain structure, acyclic dioleiins, cyclo-paraiiins,cyclic mono-oletins and cyclic diolens. Many of these hydrocarbonmixtures will also contain varying percentages of sulfur and some ofthem will also contain nitrogen or oxygen compounds.

Processes for the production of aromatic-rich hydrocarbon mixturesinclude the pyrolysis or cracking of crude petroleum, or fractionsthereof, containing at least two carbon atoms such as ethane, propane,propylene, butane, natural gasoline, light straight run gasoline,straight run naphtha, kerosene, light cycle oils produced in thecracking of gas oils to produce gasoline, straight run gas oil, etc.These processes are carried out with or without the aid of catalysts andin the presence or absence of steam. Generally, the reaction temperatureis in the neighborhood of about 1350 to 1550 F. and the pressure may befrom to 50 p.s.i.g. or higher. Such pyrolysis operations are generallycarried out primarily for the production of ethylene. The pyrolysis ofhydrocarbons to produce ethylene results in a normally gaseous product`United States Patent O containing unsaturated hydrocarbons, including,ethylene; normally liquid hydrocarbons rich in unsaturaed hydrocarbons,including, olens and diolefns of varying boiling points and structuresand various aromatic hydrocarbons; as well as tar. The normally liquidhydrocarbons and tar obtained from this process are consideredbyproducts. These by-products are removed by rapidly cooling thepyrolysis products, usually by quenching with water, to a temperature ofabout 400 F. A viscous tarry material condenses out of the gas duringthe, quenching operation. Gases from the quenching operation are thencompressed and cooled and a liquid material boiling between about and360 F. condenses out of the gases during the compression-coolingoperation. This last material is known as dripolene.

Dripolene fractions obtained in the manner set forth normally containabout two-thirds aromatics and onethird non-aromatics, the latter beingmostly oleiins and diolefins. In a typical situation dripolene willcontain about 64% aromatics consisting essentially of benzene andtoluene and about 36% non-aromatics including acyclic mono-olens,including, secondary and tertiary mono-oleiins of normal and branchchain type, acyclic diolens, cyclo-parains, cyclic mono-olens, cyclicdioleins, and, in some cases, oxygen compounds and sulfur compounds.

It has heretofore been suggested that the removal of aromatics fromdripolene and other aromatic-containing mixtures can be accomplished byselective adsorption on solid materials, such as silica-gel, activatedalumina, etc. However, such selective adsorption of aromatics isrelatively ineffective since diolens, present in the mixture, behavequite similarly to the aromatics. The other approach is, of course, theremoval of the unsaturated compounds from the aromatics. Such removal ofunsaturates has heretofore been practiced by a number of processingschemes, for example, hydration, halogenation, hydrohalogenation,carbonization, hydrogenation followed by glycol-water extraction,ozonolysis, polymerization, etc. However, because of the highconcentrations of unsaturates in mixtures of aromatics, such asdripolene, processing costs and aromatic losses due to reactivity of thearomatic compounds has generally confined the prior art treatments, atleast commercially, to hydrogenation and polymerization.

Under the conditions normally employed in the hydrogenation ofaromatic-rich mixtures, such as dripolene, including, using a palladiumcatalyst for diolelin conversion followed by a second hydrogenation andiinally the glycolwater extraction of the product, the cost ofhydrogenation is usually quite high, since large quantities of hydrogenare necessary, and the glycol-water extraction alone is an expensiveproposition. In addition, high pressures and high hydrogen tohydrocarbon ratios must be employed to produce an essentiallyolefin-free product. Under these conditions, diolens normally undergo aDiele-Alder reaction to produce polymers, gums and resins. Further, whena palladium catalyst is used it is readily poisoned by feed mixtureshaving normal sulfur contents and hydrogen containing small amounts offree hydrogen suliide.

Where polymerization is utilized for the separation of unsaturates fromaromatic mixtures, typical polymerization conditions lead to undesirablelosses of aromatics. This is caused by the alkylation of the aromatics,which takes place with approximately the same ease as thepolymerization.

Another convenient source of aromatic hydrocarbons, particularly benzeneand toluene is an aromatic light oil obtained by the high temperaturecarbonization of coal. The products of this carbonization are coke andthe aromatic light oil. This light oil contains relatively highconcentrations of unsaturates, sulfur and nitrogen compounds in additionto benzene, toluene and xylene. For example, a coal tar light oilboiling in the range of about 150-300 F. will contain, roughly, 86%benzene-toluene and about 14% unsaturates and impurities. Thenon-aromatics nintroduced to distillation column 112 where it isseparated into three fractions. A heart-cut or benzene-tolueneconcentrate boiling between about 140 and 250 F., and, preferablybetween 160 and 245 F. is separated and discharged through line 114'.l Afraction boiling below about clude acyclic mono-olens, including,secondary and ter- 5 140 F., and, preferably, below about 160 F. isdischarged tiary mono-olefins of normal and branch chain type, throughline 116. Finally, materials boiling above about acyclic diolens, cyclicparaflins, cyclic mono-olefins, 250, and, preferably, 245 F., aredischarged through cyclic dioleiins and substantial amounts of sulfurand sulline 118. The benzene-toluene concentrate passing through furcompounds as well as nitrogen compounds. line 114 is fed to a firstpolymerization zone 120. In po- Heretofore, the recovery of aromaticsfrom coal tar lymerization zone 120 the benzene-toluene concentrate islight oils, particularly the recovery of benzene, has been polymerizedunder low severity polymerization conditions. effected by acid washingwith sulfuric acid, benzene crys- Under such low severity conditionsdiolefins and tertiary tallization followed by acid washing,hydrotreating folmono-oleins undergo polymerization, with little or nolowed by solvent extraction with an aromatic-selective alkylation ofaromatics and only minor conversion of tolusolvent or hydrotreatingfollowed by high severity hydroene. In polymerization unit 120 thematerial is subjected cracking. Each of these treatments has been foundto have to a temperature of about 0 to 300 F. and, preferably, its ownpeculiar drawbacks. For example, acid treating 100 to 200 F., at apressure of 0 to 1000 p.s.i.g., and, alone results in a benzene productof high purity but havpreferably 50 to 200 p.si..g., and at a liquidhourly space ing a high thiophene content. Benzene crystallizationfolvelocity (LHSV) of about 0.1 to 10, and, preferably, 0.5 lowed byacid washing will produce a product of high to 2. Any acidic, solid,oxide catalyst, such as, silica-alupurity having a low thiophenecontent; but the recoveries mina, boria-alumina, silica-magnesia, uoridepromoted of benzene are low. Hydrotreating followed by solvent alumina,etc., may be used. The product of polymerization extraction produces ahigh purity benzene product but is unit 120 is discharged through line120. a costly process and coking problems in the preheater to Theadvantages of processing a benzene-toluene conthe hydrotreater exist.The nal technique, of hydrotreatcentrate in accordance with the presentinvention as oping followed by high severity hydrocracking, is a costlyposed to a board boiling range aromatic mixture are illuspropositionbecause of the high pressures and high temtrated by the examples in thetable which follows. The peratures involved and at times such treatmentdoes not feed material to Runs #1 and 2 was a raw dripolene conproducespecification grade benzene. taining about 52.4% benzene and 11.6%toluene. By dis- In accordance with the present invention it has beentilling the raw dripolene to recover a benzene-toluene consurprisinglydiscovered that olens may be readily recentrate or heart-cut boilingfrom 160 to 245 F., the folmoved from liquid hydrocarbon mixturescontaining, in lowing feeds to the polymerization unit were obtained forexcess of about 50% aromatics, by selectively distilling Runs #3 to 5.the mixture to recover a heart-cut rich in desired aromatics,selectively treating the heart-cut fraction to convert Run #3 #4 #5 theacyclic diolens and at least a portion 'of the acyclic Total 16H45., F6&1 7m 71.0 mono-oleins, and, finally, selectively treating at least aBenzene 15.2 12.2 16.8 portion of the product of the first selectivetreatment to 1525? convert the cyclic compounds to aromatics and any re-40 To1uerif-- 1.o 1.1 0.6 maining non-aromatic compounds to compoundshaving TABLE I Run Cata-ly# "W ""'m" H 10B203/Al203 SIGs-A1203SlOz-Alsoa 10BzO3/Alz03 SiOZ-AlgO;

0 rtig:::33:22::::::::::::::::::::::::: 83 103 SS lili l2? LHSV o 2 1 11 Pmlctogggyriiby volume ss 92 se 72 91.6 Benzene, percent by volume-.25. 8 23.5 6. 4 12. 2 12. 2 Benzene, percent by volume. 60. 0 63. 8 80.0 72. 4 73. 2 Toluene, percent by vo1ume 12. 7 11.0 13. 6 14. 3 14. 0T01uene, percent by volume 1. 4 1. 4 0. 0 1.1 0. 0

boiling points differing from the boiling range of the de- A comparisonof the results obtained in the table imsired aromatics. mediately aboveshows the superiority of the polymeriza- The details of the presentinvention can best be undertion of a benzene-toluene concentrate underthe selective stood and exempliiied by reference to the followingdeconditions of the present invention. scription when read inconjunction with the drawings, The product of polymerization reactor 120still contains wherein: substantial amounts of unsaturates which arenormally of FIG. 1 is a flow diagram of one form of the present thesecondary mono-olein-type having normal or branched invention. chains.Further polymerization of these olelins could only According to thepresent invention it has been found be accomplished under severeconditions which would quite surprisingly, that the problems ofrecovering benlead to aromatic alkylation and, thus, benzene-toluenezene and toluene from coal tar light oils can be overcome depletion.This is true since processing secondary oleiins by a novel combinationof low severity polymerization. over an acidic catalyst yields secondarycarbonium ions According to a specific technique, high purity aromaticswhich undergo polymerization or aromatic alkylation with are separatedfrom aromatic feed mixtures by selective equal facility. lf, however,this product is further polymerdistillation followed by two states oflow severity polymized under mild conditions and in the presence of atererization. The features of the technique will be more cleartiaryolefin, from an external source, these difficulties are ly understood bya specitic example illustrated in the drawing.

In accordance with the drawing, a highly aromatic feed mixture isintroduced to the system, from an external source not shown, throughline 110. The feed mixture is substantially overcome.

Accordingly, the polymer from line 122 is passed to distillation column124 where it is fractionated to separate a higher boiling productboiling above about 250 F., and, preferably, above 245 F. This highboiling material is discharged through line 126. The lower boilingportion of the polymerized material is discharged through line 128. Fromline 128, the low boiling fraction is charged to a second polymerizationzone 210. This is accomplished by closing valve 212 in line 128 andopening valve 214 in line 216. It has been found in accordance with thepresent invention, that the second polymerization unit 210 can beOperated under mild polymerization conditions to effect additionalpolymerization by introducing a tertiary olefin to polymerization unit210, from an external source (not shown) through line 218. The tertiaryolefin produces tertiary carbonium ions and shifts the driving force ofthe reaction toward polymerization as opposed to alkylation ofaromatics. Suitable olefns for this purpose include C4 to C olefins andtheir dimers, particularly isobutylene and isoamylene. The tertiaryolefin may be utilized in ratios of about 1/1-1000 volumes of olefin pervolume of feed, and, preferably, 1/10-100. The polymerization may becarried out at temperatures between about 0 and 300 F. and, preferably50 to 200 F., at a pressure of about 0 to 1000 p.s.i.g., and,preferably, 50 to 200 p.s.i.g., and at a liquid hourly space velocity(LHSV) between 0.1 and 10, and, preferably, between 0.5 and 2. Suitablecatalysts include any acidic, solid oxide catalysts, such as,silica-alumina, burla-alumina, silica-magnesia, fluoride promotedalumina, etc. Thus, essentially the same process is carried out in thesecond polymerizer as in the first with the exception of added olen. Thefollowing table shows the results of polymerizing the product of Run #5of the previous table, with and without the addition of tertiaryolefins, as set forth herein.

The effects of the addition of tertiary olefin on the polymerization isevident from the above runs. Specifically, the addition of 1% by volumeof isobutylene more than doubled the rate of disappearance of olefnsthrough polymerization. By employing larger amounts one can obtain anessentially olefin-free product. The polymer from polymerization unit210 is discharged through line 220. The polymer is then passed todistillation column 222 where materials boiling above about 250 F., and,preferably, above 245 F., are separated and discharged through line 224.The overhead from column 222 is discharged through line 226 and valve228. It then passes to line 134 and column 136, where materials boilingbelow about 176 F. benzene, and toluene are separated from the mixtureand discharged through lines 138, and 142, respectively. The benzeneand/or toluene can be further purified by a conventional hot claytreatment by passing the same through line 144 and valve 146 or line 148and valve 150, respectively, to clay treater 152. The benzene andtoluene from treater 152 may be discharged through lines 154 and 156,respectively. Alternatively, benzene can be withdrawn in advance of theclay treater through line 158 and valve 160 and toluene through line 162and valve 164. Since, the hydrocracked product normally contains lessthan about 5% by volume of undesirable products, the clay treater couldbe used ahead of column 136 to treat the entire hydrocracked product.

What is claimed is: 1. A method for recovering benzene and toluene fromnormally liquid hydrocarbon mixtures containing in excess of about fiftypercent (50%) by volume of benzene and toluene comprising:

(a) distilling said mixture to remove a benzene-toluene concentrateboiling between about 140 to 250 F.;

(b) polymerizing the concentrate of (a) at a temperature of about 0 toabout 300 F., and a pressure of about 0 to 1000 p.s.i.g. and in thepresence of an acidic, solid oxide catalyst; (c) distilling the productof (b) into a concentrate having a boiling point of about 140 to 250 F.;

(d) polymerizing the concentrate of (c) in the presence of a tertiaryolefin from an external source at a temperature of about 0 to about 300F., a pressure of about 0 to 1000 p.s.i.g. and in the presence of anacidic solid oxide catalyst; and

(e) distilling the product of (d) into a benzene and toluene fraction.

2. The method of claim 1 wherein the tertiary olefin of step (d) is a C4to C10 tertiary olefin.

References Cited UNITED STATES PATENTS 2,375,464 5/ 1945 Borden 260-674R 2,953,612 9/ 1960 Haxton et al. 260-683.9 3,294,857 12/ 1966 Tokuhisaet al. 260-674 H 3,296,120 1/ 1967 Doelp et al 260--674 H 2,733,284 1/1956 Hamner 260-674 R 2,849,512 8/ 1958 Banes et al 260-674 R 3,271,2979/ 1966 Kronig et al 260-674 H 3,400,168 9/ 1968 Fukuda et al 260-674 H3,429,804 2/ 1969 Sze et al 260-674 H 3,449,460 6/1969 Tarhan 2'60-674 ACURTIS R. DAVIS, Primary Examiner U.S. Cl. X.R. 260--674 A

